Split testing (or A/B Testing) is a standard feature in all commercial solutions. It works sending two versions (or three) of the emailing to a limited subgroup of users, it analizes the objective (click to a link, as an example) and selects the winner version to send to the rest of the list. All the process is automàtic.

Well, it is in the commercial version of OpenEMM and we call it auto-optimization. We move features from commercial to open source from time to time, but, honestly, not this one in the near future. However, the plugin interface of OpenEMM 2012 will allow for third-party extensions. Maybe someone else will implement a split feature?